A scroll compressor has a cylindrical closed vessel whose both ends are closed, and the closed vessel is arranged vertically. In the closed vessel, a refrigerant compressing section consisting of a combination of a fixed scroll and an orbiting scroll and a motor for driving the orbiting scroll are housed. The motor is also a heat source, and when it is operated in a closed space such as the closed vessel, the temperature rises rapidly. An excessive rise in temperature deteriorates component materials of the motor, so that the motor must be cooled.
In the scroll compressor, as one of the methods for preventing an excessive temperature rise of the motor, a method described in Reference 1 (Japanese Patent Application Publication No. H07-305688) is known. This method is explained with reference to FIG. 10. A scroll compressor 1 has a cylindrical closed vessel 2 whose both ends are closed, and the interior of the closed vessel 2 is divided into a compression chamber 21 and a motor chamber 22 with a main frame 4 being held therebetween.
In the compression chamber 21, a refrigerant compressing section 3 consisting of a combination of a fixed scroll 31 and an orbiting scroll 32 is housed, and in the motor chamber 22, a motor 6 having a rotational driving shaft 5 for orbiting the orbiting scroll 32 is housed. The closed vessel 2 is arranged vertically so that the axis thereof is substantially vertical, so that a bottom portion of the closed vessel 2 forms a storage portion for lubricating oil 9.
The fixed scroll 31 and the orbiting scroll 32 each have a scroll wrap formed so as to erect on an end plate, and are arranged in a state in which these scroll wraps are engaged with each other. In this state, the orbiting scroll 32 is rotated by the motor 6, by which a crescent-shaped space formed by the wraps is moved from the outer periphery to the center while the volume is decreased. By utilizing this operation, low-pressure gas is sucked from the outer periphery side and high-pressure gas is discharged from a portion near the center.
In order to restrain an excessive rise in temperature of the motor 6, in Reference 1, a pipe 23 is provided on the outside of the closed vessel 2 to cause the refrigerant compressing section 3 to communicate with a lower space 22b of the motor chamber 22, by which high-pressure refrigerant gas produced in the refrigerant compressing section 3 is introduced into the lower space 22b of the motor chamber 22 via the pipe 23.
According to this configuration, the high-pressure refrigerant gas passes through a gap Ga between a stator 6a and a rotor 6b of the motor 6 and a gap Gb between the stator 6a and the closed vessel 2, flowing toward an upper space 22a of the motor chamber 22 while cooling the motor 6, and is delivered to a refrigerating cycle through a refrigerant discharge pipe 24 provided in the upper space 22a. 
However, in the case of Reference 1, there arise problems described below. The lubricating oil 9 stored under the motor chamber 22 is pumped up by a positive displacement pump or a centrifugal pump provided on the lower end side of the rotational driving shaft 5 along with the rotation of the rotor 6b. After lubricating sliding portions such as a bearing of the main frame 4, the lubricating oil 9 returns from the upper space 22a of the motor chamber 22 to the lower space 22b thereof passing through the gap between the stator 6a and the closed vessel 2.
Therefore, on the outer peripheral side of the stator 6a, the high-pressure refrigerant gas flowing from the lower space 22b toward the upper space 22a and the lubricating oil flowing from the upper space 22a toward the lower space 22b collide with each other, so that the return of the lubricating oil 9 is hindered. Therefore, a sufficient amount of lubricating oil 9 is not supplied to the pump, so that poor lubrication of sliding portions may occur. Also, since the pipe 23 is laid on the outside of the closed vessel 2, the piping cost is needed.
To solve these problems, the applicant of the present invention has proposed a scroll compressor described in Japanese Patent Application Publication No. 2003-106272 as Reference 2. In this scroll compressor, as communicating means for causing the upper space of motor chamber to communicate with the lower space thereof, first communicating means is provided between the stator of motor and the enclosed vessel, and second communicating means is provided in the rotor of motor or in the rotating shaft thereof. A radial fan that rotates together with the rotor is provided on an upper end ring of the rotor to directly introduce the high-pressure refrigerant gas produced in the refrigerant compressing section into the upper space of the motor chamber, by which the high-pressure refrigerant is circulated by convection using the radial fan to cool the motor.
FIG. 11 shows an example of a radial fan 7 provided on an upper end ring 6c of the rotor. According to this configuration, some of high-pressure refrigerant is sucked from the lower space toward the upper space on the second communicating means side, and a circulation path for a flow from the upper space toward the lower space is formed on the first communicating means side, so that the motor can be cooled without a collision of the high-pressure refrigerant gas with the flow of lubricating oil.
In a cage rotor, the end ring is usually manufactured by casting of aluminum. In Reference 2, fan blades 7a of the radial fan 7 are formed integrally with the upper end ring 6c, and a fan cover 8a for covering the top faces of the blades 7a is integrally formed on an upper balancer 8 installed to the upper end ring 6c. 
According to this configuration, by installing the upper balancer 8 to the upper end ring 6c, the radial fan 7 can be assembled. However, since the fan blade 7a and the upper balancer 8 have the same height, the fan blade 7a is higher than is necessary. Also, the mass of the balancer 8 must be increased according to the size of the fan blade 7a, which increases the material cost.
Furthermore, since the upper balancer 8 is formed integrally with the fan cover 8a for the fan blades 7a, and thus the fan cover 8a is located just under a bearing section 4a (see FIG. 10) of the main frame 4, a space having a height larger than the height of the upper balancer 8 must be secured between the bearing section 4a and the rotor 6b, which poses a problem in that the axial length of the scroll compressor itself must accordingly be increased inevitably.
To solve this problem, the applicant of the present invention has succeedingly proposed a scroll compressor described in Japanese Patent Application No. 2002-308007 as Reference 3. One example of this proposal is explained with reference to FIG. 12. The height h of the fan blade 7a is made have the minimum height necessary for the air blowing capacity of the radial fan 7, while the upper balancer 8 is made have a height p larger than h and is arranged so as to rotate along the outer periphery of the bearing section 4a of the main frame 4.
According to this configuration, the space between the bearing section 4a and the rotor 6b can be made narrower than the height of the upper balancer 8. Therefore, the axial length of the scroll compressor itself can be made shorter, and also the radial fan 7 having a predetermined air blowing capacity can be obtained.
However, in manufacturing the fan blades 7a and the upper balancer 8, which have different heights as shown in FIG. 12, sintering is technically difficult to perform. Therefore, a cast product must be finished by cutting, which increases the manufacturing cost. A method can be used in which the radial fan 7 and the upper balancer 8 are manufactured separately by sintering. However, this method is unfavorable because the assembling man power increases, which also results in increased manufacturing cost.
Also, in a synchronous motor using a permanent magnet rotor, unlike an induction motor having the cage rotor, the fan blades cannot be molded integrally with the end ring of rotor. Therefore, the fan blades of radial fan must be manufactured as a piece part by sintering or casting, which causes the cost to increase.